Ship stabilization system



April 11, 1961 F. D. BRADDON ET AL SHIP STABILIZATION SYSTEM 6Sheets-Sheet 1 Filed June 20, 1955 INVENTORS ED. BRADDON, LEBL'AC/l,LMc//ArwcA/,m EL@ lATTORNEY April 1l, 1951 F. D. BRADDON ET A1.2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 2 ATTORNEYApril 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 5 A'ToRNEYApril 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM foo 5 g5 0MM HaR/Z 36 na/M c l IRNEY April 11,1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM 6 Sheets-Sheet 5 Filed June 20. 1955 ATTORNEYApril 11, 1961 F. D. BRADDON ET AL 2,979,010

SHIP STABILIZATION SYSTEM Filed June 20, 1955 6 Sheets-Sheet 6 ATTORNEYSHE? SEABLIZATION SYSTEM Frederick D. Braddon, Babyion, Lennox F. Beach,Sea

Ciif, and lioseph E. lhadwck, Jr., Levittown, NY.,

iiiied .inne 2.0, i955, Ser. No. 6,662 es autres. (ci. ini-ias) Thepresent invention relates generally tothe stabilization of marinevessels and more particularly to improvements in the roll stabilizationthereof by means of activated fins projecting substantially horizontallyfrom each side of the ship hull preferably at the turn of the bilge.These tins are operated-automatically and independently about normallyhorizontal axes in response to orders oriffinating in sensinginstruments which detect and meat'- ure several functions of the shipsrolling motion. These fins are operated in such a manner as thecounteract the disturbing moments applied to the ship by the action ofthe waves on the hull. The stabilizer is designed to cope with all kindsand types of sea motions that are encountered in service. The ns areangularly fully retractable or stowed in the hull when not in service.

The activated fin roll stabilization of ships has been known for a greatnumber of years hut these fins have found only limited use by the marineindustry. The success of prior systems has been impaired by twoprincipal drawbacks, viz. controlling the angle of tilt of the iin withrespect to the craft, and the large hold space required for stowing thefins when not in use. For maximum lift eifect, the lift exerted on eachside of the vessel by each fin should be equal in magnitude and oppositein sign thereby producing a pure couple about the craft metacenter orlongitudinal axis. However, in the past, the desired lift of each iinwas approximated by controlling simultaneously the angle of tilt of thens with respect to a fixed reference in the ship. Such flu angle controlin most applications is not desirable since a pure couple is notproduced. This is caused by several factors. Firstly, the lift producedat any angle of attack of the hns is roughly proportional to the squareof the speed and a n angle control system therefore requires a veryaccurate and complex control of system gain with speed. Secondly, therelation between lift and angle of attack is by no means linear.Finally, and most important, the actual angle of attack of the tins withrespect to the local sea flow direction differs radically from the angleof tilt of the blade or tins with respect to the ship. This willinevitably be the case under heavy sea conditions when maximumstabilization elfect is most desired. In fact, the false angles ofattack created by ship and wave motion may be as much as l to 20degrees, and hence may equal or even exceed the iin angles ordered forstabilization if angle control is employed. These false angles of attackhave an obviously undesirable effect on the performance of the systemand even a more serious effect on the safety and reliability of thesystem since they cause the fins to be subjected to heavy and repeatedoverload.

it is therefore the principal object of the present invention toposition the tins in such a manner as to produce the correct stabilizinglift or moment at any instant rather than a particular iin angle withrespect to the ship.

It is a further object of the present invention to position the fins inaccordance with a commanded lift, rather 2,979,010 'Patented Apr. il,i961 than in accordance with a commanded angle of tilt, by means of asignal generator or lift transducer which measures the actual liftexerted by each iin and repeat this measure back agalnst an ordered liftcommand.

Each lin is operated by means of a servomotor which is actuated by thedifference between ordered lift and actual lift and therefore the liftproduced by each` tin is held substantially equal to the ordered lift inspite of any and all false angles of attack produced by sea ilowrelative to the ship hull.

Another object of the present invention is to provide limiting means onthe ordered lift command and hence on the actual lift produced by eachiin in accordance with ships speed.

Another object of the present invention is to provide an activated iinroll stabilization system for ships wherein the tins stabilize thevessel at the apparent vertical'rather than to the actual vertical suchas provided by a vertical gyroscope. In other words, the roll anglesignals for the system are derived from a linear accelerometer orinclinometer rather than from the gyror vertical. The use of a linearaccelerometer eliminates the vertical gyro and hence the problem of longterm gyro drift. Furthermore, by stabilizing to the apparent vertical,the system operates to place the apparent gravity vector straight downthrough the deck which is the most comfortable condition for thepassengers and also the best condition for the ship in regard tostructural stresses and cargo stability. A linear accelerometer alsosenses centrifugal accelerations and hence anticipates rolling due toyaW-heel coupling effects whereby improved ship performance in followingand quartering sea conditions is obtained under which conditions theWave frequency becomes very low with respect to the ship due toshipsspeed and approaches resonance with the ships natural frequency.

Another object of the present invention'is to provide a rollstabilization system of the above character wherein roll rate, asmeasured by a rate gyroscope, is the primary control term, the basicroll rate signal being supplemented by signals proportional to rollangle and roll acceleration, the former being useful in improving shipperformance in following and quartering seas, i.e.,'seas coming fromabaft the beam and the latter being useful in meeting the impact effectof bow and head seas, i.e., seascoming from forward of the beam.

All of the above objects of the present invention contribute to a moreefficient roll stabilization system employing activated tins than hasheretofore been available in prior systems of this general character.

A further disadvantage of prior activated roll iin stabilization systemsfor marine Vessels is the excessiveamount of space required for the iinoperating gear; also the excessive space required for the stowage of theiinY when not in use. Heretofore, the tins have been stowed byretracting them axially on the axis about which the iin pivots, i.e.,the fins are retracted alongV a substantially athwartship axis. Afurther disadvantage resulting from axial stowing is that the iinactuating torques must be applied through long shafts and are thereforesubject to shaft torsion errors.y Furthermore, such prior stowingsystems and methods in many cases required a free accessible hold spacewhich extended completely through the beam of the ship thereby requiringexcessive modification of the internal hull structure.

Therefore, another principal object of the present invention is toprovide a method and apparatus for stowing the tins which requires aminimum storage space for the iin and a minimum space for the iincontrol gear.

it is a further object of the present invention to provide stowingapparatus for the tins which is more contpact and lightweight andtherefore saves valuable space in the hull. These latter objects areachieved by angularly retracting the tins into hull boxes which extendfore and aft along the ships side rather than athwartship. This designnot only allows a considerable saving 1n space and weight but provides atighter positioning system in that linkages and shaft lengths betweenthe tilting ram and the fin are held to a minimum.

It is a further object of the present invention to mount the iin on asubstantially horizontal shaft mounted in a housing for rotation about asubstantially horizontal, ie., athwartship axis, the housing in turnbeing mounted on stub shafts for rotation about a substantially verticalaxis. The first shaft tilts the iin for stabilization purposes and thesecond shaft rotates the housing and iin into the side of the hull forstowing purposes. Generally, the activated fin roll stabilization systemof the present invention consists of fins mounted on each side of thevessel. Each iin may be of conventional hydrofoll design and may employa full iiap for increasing hydrodynamic efiiciency similar to the brakeiiaps used on aircraft to effect increased lift. The stabilizing momentis obtained by controlling the angle of attack by use of a fast responsehydraulic servo system for each iin. The fins are retracted into theships hull by foldling longitudinally when not in service. Ship motionsare measured by means of a rate gyro, an inclinometer or lateralaccelerometer, and an angular accelerometer. These instruments -and theassociated circuits continuously compute the required stabilizing momentor iin lift and the hydraulic servo simultaneously maintains the iinangle such that the actual lift as measured by the iin stress isbalanced to the ordered value. The objects of the present invention setforth above may be summarized as follows:

" (a) To provide roll stabilization by controlling iin lift rather thaniin angle;

(b) To provide stabilization of the craft to the apparent verticalrather than the actual vertical;

V(c) To provide n actuating gear which is more cornpalct and thereforerequires a minimum of hull space; an

(d) To provide an improved system of iin retraction and stowage.

Other objects and advantages of the present invention not at this timeparticularly enumerated will become apparent as a detailed descriptionof a preferred embodiment thereof proceeds, reference being made to theattached drawings, wherein:

Y Fig. is a schematic diagram of the system of the present mvention;

` Fig. 2 is a schematic cross-sectional view of a ship showing the-relative position of the fins in the hull and the ship motion sensingdevices employed for controlling the same;

Fig. 3 is a top plan view of the n actuating gear showing the iin in itsextended or rigged out position;

Fig. 4 is a vertical sectional view of the fin tilting gear showing theiin in its stowed position;

Fig. 5 is a horizontal sectional view of the iin in its stowed positionin the lin box, the view being taken along lines 5-5 of Fig. 4;

Fig. 6 is a vertical sectional view of the fin shaft housing taken alongthe lines 6 6 of Fig. 3;

Figs. 7 and 8 are elevational views of the side of the ships hullshowing the tins in their rigged out and stowed positions respectively;

Fig. 9 is a sectional view of a suitable signal pick-off or signalgenerator for providing a signal proportional to the lift of the fin;

Figs. 10, 11 and 12 are views illustrating a modification of the lifttransducer.

Referring now particularly to Figs. 1 and 2, the activated roll nstabilization system of the present invention consists generally of twofins and 21, one projecting horizontally from each side of the ship. Itwill be understood, however, that a plurality of tins on each 4 side ofthe vessel may be employed depending upon the size and speed of the shipupon which the n installation is to be made. Furthermore, the tins mayhave a slight downward inclination relative to the beam of the ship andthe term horizontally as used in this specification is intended toinclude. this slight downward tilt which may be on the order of 0 to 2Odegrees relative to the horizontal. Each tin is provided with afull-span flap 22 and 23 respectively (23 not shown) which will increasethe maximum lift of each fm and thereby minimize the space and weight ofthe installation. Such flap will also tend to reduce the average drag ofthe iin by reducing the wetted area. Each n has an aspect ratio ofapproximately 2.0 thereby providing a 'reasonable compromise betweeninduced drag and bending stress in the iin mounting shaft. The iin maybe of any of a number of known constructions and is shown as being of aconventional spar and rib construction with an al1-welded steel skin(see Fig. 6). The iins are operated automatically and independentlyabout normally substantially horizontal axes 24 (Fig. l) in response toorders originating at sensing instruments mounted in a suitable controlpanel or console in the wheel house or bridge'forming a part of theships superstructure schematically Indicated at 25 in Fig. 2. Thesesensing elements detect and measure displacement, rate and accelerationof the ships rolling motion and produce signals proportional to shipsmotions produced by all types of sea motions encountered in service. Thefins are operated through electro-hydraulic servo systems in such amanner as to counteract the disturbing moments applied to the ship bywave action.

Each iin 2G, 21 is operated in tilt by a hydraulic ram 26 abouthorizontal axis 24, which cylinder in turn is controlled by a variabledelivery hydraulic pump 27., the operation of which is controlled inaccordance with a computed lift command through command servo system 28.The stowing or rigging out of each iin is accomplished by two hydrauliccylinders 29, 30 operated by solenoid valve 31 using oil supplied froman auxiliary pump 32 (Fig. 3). Stowing rams 29 and 30 operate to rotatethe tins about a substantially vertical axis so that. the fins arestowed by angularly folding them longitudinally into suitable iin boxesin the hull. A manual hydraulic pump control for either axis may beprovided in the event of complete electrical power failure. lt should benoted that the two fin assemblies operate completely independently ofeach other with no mechanical or hydraulic connection between theassemblies. The iin tilt servo system consists generally of the variabledelivery pump 27 driven by an electric motor 33, an electric motorstroke servomotor 34 which is driven from the output of a magnetic servoampliiier 35 receiving a lift command signal from the sensing elementsland lift signal servo loop 36. The lift command servo loop 36 ispreferably mounted at the ships bridge in a suitable console containingsensing elements which measure roll angle and its time derivative. Itwill be noted that the lift command servo operates two separate signalgenerators, one of which .is shown at 37, which supply separate liftorder signals to each of the fin actuating servo systems. In Fig. l onlythe port stabilizing iin and actuating means therefor is illustrtaed, itbeing understood that the starboard iin actuating means is exactly thesame, except that the tin structure and operating apparatus are mirrorimages. Furthermore, the output of servo loop 36 drives two signalgenerators, i.e., synchro generator 3'7 for supplying the lift commandsignal to the port iin mechanism and another similar synchro (not shown)which supplies a separate signal degrees out-of-phase to the signal fromsynchro 37 to the starboard iin actuating mechanism. Hence there are twoindependent iin positioning servos having the same ordered lift incommon.

The lift Vcommand signal for controlling the motion of the stabilizingtin is a composite or summation of three signals separately generatedthrough the effects of ship motion on the signal generating devices.These three signals include a signal proportional to the roll angle ofthe craft, a signal proportional to the roll rate of the craft, and oneproportional to roll acceleration of the craft. The roll angle componentof the lift command signal is provided by means of a linearaccelerometer 39 of conventional form mounted with its sensitive axisdisposed athwartship having any suitable signal generating means adaptedto provide an alternating current output having a phase depending uponthe direction of roll of the ship and an amplitude depending on themagnitude of such motion. The effect of this linear accelerometer orinclinometer signal is to provide static and low-frequency stabilizationof the craft to the apparent vertical rather than the true vertical. Thelinear accelerometer also senses centrifugal acceleration and henceanticipates craft rolling due to yaw-heel coupling, i.e., the tendencyof the craft to heel as the craft turns. The physical significance ofthis signal component of the ordered lift signal proportional to rollangle is to increase the effective GM of the ship without at the sametime increasing the moment acting on the ship produced by a given waveslope, as an actual or physical increase in .the GM of the ship woulddo. The GM of the ship may be defined as the distance between the centerof gravity of the ship and the metacenter thereof (see Fig. 2).

The lift command signal component proportional to roll rate is providedby means of a conventional rate gyro 4t) which is mounted in the craftsuch that precession thereof occurs upon rolling of the craft about itslongitudinal axis, i.e., about its metacenter. A signal-proportional tothe angle through which the gyro processes may be supp-lied by means ofany suitable type signal gene-rator 41 which produces an alternatingcurrent output of phase depending upon the direction of rolling motionof the ship and of an amplitude depending upon the magnitude of suchmotion. The physical significance of the roll rate signal in thecomposite lift command signal is that it increases the effective dampingof the ship in response to rolling motion thereof produced by waveaction. This signal proportional .to ships roll rate is the primarycontrol signal because a ship in its natural state is highlyunder-damped in roll and hence the principal need is for roll damping.

The third signal, i.e., roll acceleration signal, is provided by meansof lan angular accelerometer 42 of conventional form which is providedwith a suitable pick-off device .3 which generates a signal having aphase in amplitude proportional respectively to the direction an amountof angular acceleration of the craft about its longitudinal axis. Thephysical significance of the ro-ll acceleration signal component of theordered lift signal on craft operation is to effectively increase themoment of inertia of the craft about its longitudinal axis.

Hence, the roll angle signal and the roll acceleration signal aresubsidiary signals that improve performance under extreme conditions ofhigh or low Wave frequencies. As above stated, because the roll angledetecto-r is actually an apparent vertical detector, it also sensescentrifugal accelerations due to yaW rate and thereby provides improvedperformance of the ship in following seas.

The roll angle, roll rate, and roll acceleration signals are appliedrespectively to the windings of potentiometers 44, 45 and 46, theoutputs of which are combined in magnetic amplifier 47 which forms apart of the command signal servo loop 36. The sum of the above threesignals drives an electric servomotor 4S, the output of which positonscommand signal generator 37 through a limit stop apparatus 51 and slipclutch 49. In order that the output shaft S of servo loop 36 correspondexactly to the sum of the acceleration, rate, and displace.- mentsignal, a position feedback signal is generated in feedback synchro 55,the output of which is applied to the input of amplifier 47. A meter 56may be connected to sense the feedback signal for providing an .operatorwith an indication of the magnitude'Y of .the ordered lift commanded bythe lift command servo loop 36.

As illustrated in Fig. l, several external adjustments are provided forincreasing the -versatility of the stabilization system of the presentinvention. A list correction control is provided to buck out anyconstant roll angle that might be present. This is accomplished by meansof a knob or control handle 57 which actuates through an eccentric 5S tovary the neutral axis of linear acceler ometer 39. For this purposeaccelerometer 39 is mounted on a platform 59 pivotally secured to thecraft by means of hinge 60 for rotation about an axis parallel to thecraft longitudinal axis. This list correction control is providedbecause it is not economical to use the stabilizing tins as a means fortrimming out any permanent 11st of the vessel. it will be understood, ofcourse, that under emergency conditions the system may be so used.

In order that the control sensitivity of the system may be adjusted forthe purpose of conforming with the requirments of various sea conditionsthat are encountered, a sea state selector or weather adjustment isprovided. In the presen-t embodiment, a knob 61 adjusts the magnitude ofthe input signals to amplifier 47 by adjusting the wipers ofpotentiometers 44, 45, 46 simultaneously.

The limiter device 51 on the output shaft of servomotor 48 is for thepurpose of limiting the ordered lift signal as a function of craft speedsince the effectiveness of the fin in producing roll moments about thecraft longitudinal axis varies as a function of craft speed. Thus athigh speeds smaller command lift signals must be supplied to the finsand viceversa. The speed adjustment is provided by means of a knob 62which adjusts the limits stops `63 and hence the magnitude of movementof shaft 5ft. A slip clutch 49 is provided for preventing overload ofthe servomotor 48 after the limits have been reached. Speed selectorknob 62 also controls certain of the sensitivities in the iinpositioning servo systems so that these servos operate at an optimummanner at all times, as will be hereinafter described. It will be notedthat all of the sensing devices for the lift command computer or servoloop 36 are spring centered and are hence free from mechanical driftwhich might otherwise be a problem as would be the case if a position ordisplacement type gyro were employed. Furthermore, it will be noted thatelectrical drift is eliminated by the use of A.C. signals throughout.

ln the illustrated embodiment of the present invention all of theapparatus shown at the left of amplifier 35 may be included in a consolemounted on a bridge bulkhead or mounted if desired, on a pedestal at thebridge station. The portion of Fig. l to the right of and includingamplifier 35 is located at the n sites in the ships hull and thus itwill be seen that the two fins operate completely independently of eachother but are controlled in accordance with the same lift order. Theoutput of ampiifier 35 which is proportional to the difference betweenthe ordered lift and the actual lift of the fin is applied to strokeservomotor 34 which actuates through gearing 7G, slip clutch 71, andlever 72, to stroke control lever 73 of variable delivery pump 27. Astroke feedback synchro 74 is provided for insuring that the position ofstroke rod 73 of variable delivery pump 27 corresponds to the errorsignal applied to the amplifier 35. A speed feedback signal may befurther employed for insuring smooth and rapid operation of the strokecontrol servo loop. A tachometer 75 gearedto the output shaft of strokeservo 34 is provided for this purpose.

The output of variable delivery pump 27 is applied to iin tilting ram 26which ram rotates tin 2i) about axis 24 through crank 76 and n stubshaft 77. Ram 26 continues to rotate fin 20 until water pressure on thelatter produces a lift which is equal and opposite to that commanded. Asignal proportional to ythis lift force is generated by means of a liftsignal transducer 78 which is fed back through lead 79 to the input ofamplifier 7 3S. The mechanical structure of lift transducer 7S and itsactuating means will be hereinafter more fully described.

The operation of the iin Itilt servo loop is as follows:

the ordered lift signal from the bridge control station 25 -A and theactual fin lift signal from the lift transducer 78 are applied to servoamplifier 35 which supplies an output proportional to the differencebetween these signals, i.e., lift error. Servomotor 34 is energized bythis output and positions stroke lever '73 until the stroke positionfeedback synchro 74 supplies a signal which is equal and opposite 4tothe lift error signal. As n position is applied through ram 26, theincrease or decrease in actual fin lift will result in a signal fromlift transducer 73 which gradually replaces the stroke position feedbacksignal and cancels the ordered lift signal. As the actual liftapproaches the ordered lift, the pump stroke arm 73 returns to itsneutral or zero position. When the actual 'and ordered lift signals areequal and opposite, the pump stroke remains stationary. Thus, the pumpstroke feedback synchro signal stabilizes the servo system by preventingany over-shooting of the ordered lift. Further assistance in assuringsmooth, non-oscillatory iin operation is obtained from the strokevelocity tach generator 75 'as described. While the ordered lift islimited on an absolute basis in accordance with craft speed by means oflimit stops 51, 63, local conditions at each iin require lfurther limitstops to prevent greater iin angles than are physically possible. Asillustrated in Fig. 1, completely mechanical means are provided forlimiting the mechanical operation of the iin. If the ordered liftcommand tends to produce a fin deflection of greater magnitude than ismechanically possible, a projection 8b on the end of ram piston shaft S1contacts one or the other of two projections 32 associated withbell-crank 83 which through the link S4 positions stops 85 cooperablewith stroke arm 73 to thereby limit the motion of the latter. Thus, thelatter limit stop arrangement overpowers all other orders to the pumpstroke arm 73 of variable delivery pump 27.

In order that the stroke positioning servo system operation be optimumfor all craft speeds, the speed selector knob 62 aiso controls thesensitivity of the iin positioning servo loop by controlling,throughshaft 86 and pov tentiometer S7, the energization voltage appliedto stroke yfeedback synchro 74. in this manner the sensitivity of thestroke positioning servo system is also controlled as a function ofcraft speed.

The structural details and design of the fin actuating and stowingmechanisms and the stowing compartments are illustrated in detail inFigs. 3 to S, inclusive. As shown in Figs. and 6, the iin 20 is boltedor otherwise rigidly secured to a short, hollow shaft or trunnion 77which is journaled in spaced bearings 89, 90 in a substantiallycylindrical housing 91 for rotation about tilt axis 24. Housing 91 inturn is provided with upper and lower stub shafts 92, 93, respectively,for rotation about a substantially vertical axis 3S, preferably at rightangles to the axis of rotation of iin 20 in suitable bearings 94, 9S(Fig. 4) in the upper and lower surfaces of a water-tight n actuatingmechanism box defined by walls 96, 97, 98 and 99. Since this iin box isfilled with sea water, suitable hydraulic seals 100 and 161 are providedfor preventing sea water from entering the ships hull. in thisconnection, housing 91 is provided with suitable hydraulic seals 102 forpreventing sea water from entering this housing. To further insure thatno sea water enters the housing 91, it may be completely filled with oilfrom a sump (not shown) which is maintained under a pressure justgreater than the pressure of the sea water at iin depth.

Lift forces or loads produced by the iin 20 are transmitted to thehousing 91 through horizontally spaced. bearings 89 and 90 and thence toships hull through stub shafts 92 and 93 and vertically spaced bearings94 and 95. The boxes may beY suitably reinforced in any coni ventionalmanner by means of plates and stieners.

Mounted on the upper stub shaft of housing 91 is a plate havingformedthereon a cross-head 106 to which stowing ram pistons areattached. This plate further carries a verticalcylinder 107 to the topof which is secured the n tilting ram 26. Connected with the piston 10Sof ram 26 is a 'cylindrical cross-head 109 which slides within cylinder107 and pivotally mounted there-in is a connecting rod 110 which extendsdownwardly therefrom and is pivotally connected as at 111 to crank 76which forms a part of iin actuating shaft 77.

Thus, with the fin rigged out, motion of piston 108 in ram 26 istransmitted through cross-head 109 and connecting rod 110 to pivot iin20 about axis 24 (Fig. 1) through crank 76. Controlled oil pressure fromvariable delivery pump 27 is applied to ram 26 through suitablehydraulic connections 113 and hydraulic slip rings 114, therebypermitting the entire ram 26 to rotate about vertical axis 38 withoutthe requirement of yany flexible tubing, etc.

The mechanical linkage limit stop mechanism described with respect toFig. 1 is illustrated in more detail in Figs. 3 and 4. As shown, thislimit stop mechanism is enclosed in a housing 115 which is mounted infixed relation with respect to top plate 105 and ram 26 by means of asuitable mounting bracket (not shown) which may be secured to the deckor fixed upper ange 122 of bearing 94. Ram motion is imparted to limitstop mechanism v11S by me-ans of yoke 116 and shaft 117. The operationand structure of the limit stop mechanism has been described above,reference being made to Fig. l, and corresponding numbers therein havebeen applied to corresponding parts of Figs. 3 and 4. Furthermore, thestroke servomotor 34, tachometer 75, stroke feedback synchro 7d, gearing70, clutch '71 and link 72 are all conveniently packaged in ya commonhousing 118 of Fig. 3.

In Figs. 6 and 9, there is shown a means for providing a signalproportional to the amount of lift being produced on the ship by thefins. As illustrated, the fins 20 being rigidly bolted to horizontalshaft 77, this shaft is subjected to the entire stress produced by wateraction on the iin. In the illustrated embodiment of the presentinvention, means have been provided for measuring this stress. `A discis rigidly secured, as by welding, to the inner surface of shaft 88 andis positioned as near as convenient to the outboard end thereof. Rigidlysecured to this plate, as by bolting, is a cantilever beam 121 whichextends substantially axially of the shaft toward the opposite orinboard end thereof. Rigidly and preferably vertically adjustablysecured to the end of the shaft 77 adjacent the free end of beam 121 andcooperable therewith is pick-off device or lift transducer 78. It willbe noted, partlcularly with reference to Figs. 4 and 6 that this lifttransducer' 73 is mounted in shaft 77 so that it is aligned with anormally vertical axis. Withl this arrangement, the signal generatedthereby includes only the normal component of the strain or stressimposed upon shaft 77 thereby eliminating in the actual life signal anycomponent produced by tangential forces imposed on the fin, i.e., drag.Cantilever 121 will be deected only upon stresses imparted to n supportshaft 77, which stresses will be measured by means of pick-olf 7S toprovide a signal proportional to the lift being imparted to the ship bythe iin.

Any suitable type of pick-off may be employed and one form thereof isillustrated in Fig. 9. As shown, this pickoff is an inductive pick-offdevice which comprises a threaded casing adjustably threaded in shaft 77which has fixed thereto a pick-off core and windings 124 of the Etransformer type. Two such cores are provided for failsafe purposes. Aspring loaded plunger 125 having al1 armature 1261s operated by movementof cantilever 121:`

which generates in the output winding of the pick-off a signalproportional to the stresses in shaft 77, and since stress is producedby the lift of the 1in, the signal is, therefore, proportional to thelift being imparted to the ship by the fin. This signal, as describedabove, is compared with the ordered lift command and the iin tiltingservo system reduces the difference therebetween to zero, therebypositioning the iin until the actual lift is equal to the commandedlift.

At this time it should be pointed out that another important function ofthe iin tilting servo system is its regulator action, i.e., iteliminates the elect of extraneous lift forces due to extraneousdisturbances in the angle of attack of the tin. For example, if the iinservos are in operation but for some reason no lift is ordered, the finswould go through continuous motions depending on seaway conditions,thereby eliminating the effect of local false angles of attack. Asstated above, these false angles of attack, due to local currents aboutthe ships hull, can be :as large as l to 15 degrees under severe seaconditions. Obviously, if these disturbances are not eliminated, therewill not be a very close correspondence between the ordered lift andactual lift,

In accordance with one of the important objects of the presentinvention, means are provided for angularly stowing the fins when not inuse. For this purpose, an aft extension 13 of the tin actuatingmechanism box is provided in the ships hull for accommodating the iinwhen in a stowed position, as shown more particularly in Fig. 5. Whenthe iin is in a stowed position, a failing plate 104 is provided forpreventing turbulence around the lin box. The stowing of the n iscontrolled by solenoid operated fin stowing control valve 31 (Fig. l)which controls hydraulic pressure supplied by pump 32 to stowingcylinders or rams 29 and 30 through hydraulic lines 29', 30. These ramsact in opposition as by means of crossed flexible hydraulic lines 13S,139 (see Fig. 3). The output rods 140 and 141 of rams 138 and 139 areconnected to cross-head 106 which rotate housing 91 about vertical axis3S to thereby stow or rig out the ins. However, before `such stowing cantake place, the iin must be locked in a predetermined or neutralposition with respect to the ships hull. For this purpose a synchrodevice 130 or other suitable signal generator (see Fig. 1) is providedfor measuring the yactual angle of the ns with respect to the hull, thezero position of synchro 130 corresponding to a level or zero-detiectionposition of the tins. This synchro is positioned by means of feedbackshaft 81 in the schematic of Fig. l. As shown in more detail in Fig. 4,feedback shaft 117 is provided with a rack portion 131 which engagespinion 132 for positioning synchro 130 in accordance with n position.When a stowing operation is to be initiated, the ordered n lift signalis severed from the input to amplifier 35 as by means of a suitablestowing switch 133. At the same time this switch substitutes the outputof synchro 130 for the lift command signal. Thus, if the iin is notcentralized, the lin tilting servo will drive the fin towards its zeroposition.

The finis locked in its zero-deflection position by means oflink-coupled, spring-loaded latches 134 and 135 (Fig. 4) which, duringnormal operation of the system, are held in the position shown by meansof hydraulic pressure supplied by source 32. Upon initiation of astowing operation this hydraulic pressure is cut ofi, allowing spring136 to force latches 134 and 135 into the cylinder 107. As the iinpositioning servo drives the n toward its zero position, a shoulder 137on cross-head 109 is engaged by one or the other of the extendedlatches, arresting movement of cross-head 109 and thereby securing thefin in its zero position. Since there is no position feedback, i.e., thesynchro 130 provides the only control of ram position, the ram 26 willtend to drive cross-head 109 through the zero position. The stowing ofthe fin may be continued after locking the fins.

As shown in Fig. 3, means are provided for locking the lin in its stowedor rigged out position. For locking the tin in its rigged out position,spring-loaded, hydraulically actuated latches 142, 143 engage cross-head106 when in its full clockwise, as seen in Fig. 3, position asdetermined by means of mechanical stops 144 and 145. A switch 146 isprovided for actuating an indicator in the control console in the bridgeand/or at the n site for indicating to the operator that the iin hasreached its fully extended position and is locked therein by latches 142and 143. Similarly, latch 148 is provided for locking cross-head 106 andhence iin 20 in its fully stowed position, as indicated by the dottedlines in Fig. 3. A similar switch 149 is provided for indicating thatthe finis stowed.

After the iin tilting servo system has positioned iin 20 in itshorizontal position and locks 134 and 135 have been engaged withcross-head 109 to maintain the tin in this position, latches 142 and 143are disengaged as by means of small hydraulic rams 151, 152 whichoperate through suitable linkages 153 to withdraw the latches lfromcontact with the cross-head 106. A slight rig-out pressure from rams 29and 30 may be provided to insure release of the latches. Hydraulicpressure is then applied through lin stowing control valve 31 to stowingcylinders 2,9 and 30 to cause rotation of cross-head 196 and hence fin20 in a counterclockwise direction, as seen in Fig. 3, to stow the iin20 into the iin box 103 in the hull. When iin 20 has reached its fullystowed position, crosshead 106 abuts stop 154 and the spring-loadedlatch 148 engages the cross-head to maintain it in this locked position.This latch 148 may be the same as latches 142 and 143 and may besimilarly released upon a rig-out operation.

The entire rigging-out and stowing operations may be controlled remotelyfrom the bridge control console. However, it may be more practical andmore convenient, equipment-wise, 'to rig out and stow each iinseparately at the fin sites in the hull by suitable manually controlledswitches, such as by switches 133 and 133. Furthermore, in order toprevent premature or inadvertent operation of any event in the iinrigging out or stowing cycles, suitable interlocking controls may beprovided. For example, switches associated with the centering latches134, for fin tilting ram 26 may be provided for preventing operation ofthe lin stowing control valve 31 prior to centering the switches maycomplete circuits allowing solenoid controlled iin stowing control valve31 to be operated. Further interlocking switches may be associated withlatches 142 and 143 which may be in series with the switches associatedlatches 134 and 135 whereby to prevent operation of iin stowing controlvalve 31 until the latches 142, 143 are released. It will be noted thatthe source of hydraulic power for the stowing rams 29 and 30 and for thehydraulic latch releases is supplied by the same motor which drives thevariable delivery pump 27. Therefore, in order to prevent any pressurebuild up on either side of the locked tilting ram piston 108 duringrigging out or stowing of the ns, solenoid controlled by-pass valve 160electrically interlocked with latches 134 and 135 is provided. The uppersurfaces of the 1in actuating mechanism box and the fin box 103 providea convenient space for all of the fin-operating gear, hydraulicequipment, control instruments, stowing consoles, etc.. thereby keepingto a minimum the space required for the entire iin and fin actuatingmechanism.

As described above, iin 20 is provided with a full flap 22 which is soconnected to the iin actuating mechanism that it moves in the samedirection but through a `greater angle than movement of the main iin 20,for the purpose of increasing the hydrodynamic efficiency of the iin.For this purpose an extension 155 (see Fig. 7) is preferably integrallyformed with housing 91 which carries a pin or stud 156 thereon. Sincethe housing 91 is fixed with respect to the n 20, the stud 156 is alsoxed with respect thereto. Projecting forwardly from the hinge pivotY157- E 1l orthe Hap 22 is a fork 158 whichengages stud 156. Thus, uponrotation of iin 20 about axis 24, flap 22 is caused to rotate in thesame direction but through a greater angle than iin 20 throughV therestraint on fork member 158 imposed by xed stud 156. This action isclearly indicated in Fig. 7.

ln Figs. l0, 1l and l2 there isillustrated a modification of the meansfor providing a measure of the actual lift being exerted on the shipshull by the ns. It will be noted that the general arrangement of the iinmounting structure remains essentially the same as that shown in Figs.4, 5, and 6. As shown schematically in Fig. the fin is pivotally mountedin housing 91 for moving about horizontal axis 24, the verticallyextending stub shaft 92 and 93 thereon supporting the housing forrotation about vertical axis 38 in lower and upper bearings 93 and 94.As in the apparatus of Fig. 4l, the upper bearing 94 is designed tosupport substantially the entire Vertical load of the housing 91, thelower bearing 93 being subjected substantially only to the lateral loadsproduced by water forces on the iin 2G, i.e., lift forces and dragforces.

In the present modification, it is the horizontal and athwartshipcomponent of these lateral loads which is weighed or measured to obtaina signal proportional to the vertical lift exerted on the hull by the n20. For this purpose, the outer race 162 and its support ring 165 oflower bearing 95 are not rigidly secured to the ships structure as inFig. 4, but are flexibly fastened thereto as by means of radiallyextending webs or anges 163, 164. These ilanges form a preferablyintegral part of outer race support ring 165 and extend radiallytherefrom in a direction parallel to the longitudinal axis of the shipshull. These flanges are in effect extremely stift springs 'which arecapable of transferring the lifting moment of the fins Ztl to the hullbut on the other hand in doing so will be deflected by the lift force.Since the anges are rigid along their support axis, i.e., with respectto the ships fore and aft or longitudinal axis, the deflection of stubshafts 92 and 93 is in a direction substantially athwartship or at rightangles to the ships longitudinal axis. Thus, the lift transducer 167 ispositioned with its sensitive axis along this athwartship axis andbetween the ring 165 and lower bearing housing 166. As clearly shown inFig. ll, two such transducers are employed for fail-safe purposes. Thesignal generator or lift transducer 167 is preferably of the inductiontype and may be similar to the one illustrated in detail in Fig. 9.

It will be understood, or" course, that the actual movement of the lowerstub shaft 93 with respect to the bear- -ing housing 166 is very, verysmall, i.e., on the order of a few thousandths of an inch, and hence theupper and lower uid seals 100 will be completely unaifected by suchmovement.

One of the advantages of the modification illustrated in Figs. l0, lland l2, is that the litt transducer is readily accessible Within theships hull and is, therefore, easily repaired or replaced if for somereason it become defective. Another advantage of this modiiicationresides in the fact that the lift transducer is sensitive to only thetruly vertical loads on the ship produced by n 20 and is independent ofthe angle of tilt of the tins. Thus, the lift transducer signal, i.e.,the lift repeatback signal, is exactly proportional to the vertical liftexerted `by the ns.

In regard to the iin tilt servo loop 28 which actuates the iin 2t), itmay be desirable to add to the lift feedback signal, a predeterminedsmall amount of fin angle signal whereby to provide additional stabilityto this loop. For this purpose, a potentiometer 170 is energized by theoutput of signal generator or angular synchro 13% which, as describedabove, is positioned in accordance with iin angle. The variable tap ofpotentiometer 170 is combined, through a suitable mixing circuit 171,with the'lift s ignal from 'lift transducer 78, the output thereofYbeing awa-01o supplied as a combined repeatback signal proportional toiin lift and iin angle to the input of ampliiier 35.

, It will be understood that the lift repeatback signal may be generatedin a number of different ways and by a number of different types of lifttransducers. lt may be generated by means of strain gauges which may beiixed to the fm itself or to any other element of the liu supportassembly which transmits the lift produced by the iin to the shipsstructure and is therefore subjected to stress; for example, one or morestrain gauges may be bonded or otherwise secured to the external orinternal surface of the iin Vsupport shaft 77. Alternatively, the iinsurface mayA be provided with a exible diaphragm extending alongsubstantially the entire length thereof such that flexure of thediaphragm by water pressure produces a signal output proportional to theaverage lift being produced by the n. Other means for providing a signalproportional to the magnitude of the lift being exerted on the craftbythe iin may be envisioned by those skilled in the art.

Furthermore, although in the foregoing description of a preferredembodiment of the present invention, the fins are shown and described asextending substantially horizontally from the side or bilge of the ship,it will be understood that it is within the scope of the invention inits broader aspects, that the ns may extend substantially verticallydownward from lthe ships bottom, the deflection thereof producing asimilar righting couple thereon.

Also, it should be understood that the ships motion sensing devices,instead of being located at the bridge console, may be mounted belowdecks, preferably at the n location thereby placing the signal sourcesand the apparatus responsive thereto close together. Also at such alocation, ships vibrations are at a minimum, lateral accelerations dueto roll are very small, weather conditions are no problem, and spacelimitations are not critical.

From the foregoing description and from an inspection of the attacheddrawings, it will be noted that the iin assembly box consists of afabricated box with the upper and lower bearing walls 96 and 98, theside walls 97 and 99, and the fore and aft side walls 99 and 103'forming an integral unitary structure. Assembled within the box are theiin 20 and fin linkage 112, connecting rod 110, cross-head 109, andcross-head guide or cylinder la7. The machinery deck, i.e., the uppersurface of top wall 96 has assembled thereon the stowing cylinder yokeor cross-head `106, with its latches and stops, all located andassembled, and the stowing cylinders 29 and 30 completely assembled andmounted. The top plate 96 also supports, completely assembled, the iinactuating controls, Le., the variable pump 27, with its stroke servo1118 and controls, power motor 33, and auxiliary pump 32., This lntegralassembly may be completely tested prior to transportation andinstallation. The assembly is designed for convenient mounting, as 'aunit, on a standard railroad ilat car for convenient transportation.More importantly, ythe completed assembly may be conveniently slidthrough a suitable rectangular opening in the shipsv hull and welded inplace, after which the shell plating and doub ling plate may be secured.Such complete prefabrication not only facilitates installation butgreatly cuts installation time, an important factor especially when theinstallation is on a dry-docked vessel. 1

Since many changes could be made in the above cou struction and manyapparently Widely different embodiments of this invention could be madeWithout departing from the scope thereof, it is intended that all mattercontamed in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a` limiting sense.

What is claimed is:

l. In a ship stabilization system, a n, mounting means for supportingsaid n on a ship to rotate about an axis extending generallylongitudinally of said iin and nora mally in a generally athwartshipdirection, drive means having an output coupled with said iin forrotating the same about said axis, means for producing a signal inaccordance with rolling motions of said ship, means coupled with saidiin for obtaining a repeat-back signal proportional to the lift exertedby said iin, control means coupled with said drive`means and responsiveto both said signals for controlling said drive means in accordance withthe algebraic sum thereof whereby to produce a displacement of said tinin accordance with the lift exerted thereby, means for limiting themaximum value of the signal controlling said drive means, and furthermeans coupled with said drive means for limiting the maximumdisplacement output of said drive means independently of the liftexerted by said nn.

2. In a ship stabilization system, a iin, a tirst mounting means forsupporting said tin on a ship to rotate about a first axis extendinggenerally longitudinally of said iin and normally in a generallyathwartship direction, a second mounting means for supporting said iinto pivot about a secondaxis normally extending in a generally verticaldirection, a first drive means coupled with said first mounting meansfor rotating said Viin about said first axis and a second drive meanscoupled with said second mounting means for pivoting said iin about saidsecond axis, means for respectively controlling the operation of saidfirst and second drive means, means for producing a signal in accordancewith rolling motions of said ship, means for providing a signalproportional to the position of said iin about said rst axis, means forobtaining a repeat-back signal proportional to the lift exerted by saidiin, control means for controlling said first lin-driving means inaccordance with said roll-motion, position, and lift signals, means forselectively controlling said iirst iindriving means in accordance withsaid n position signal only, and means responsive to the operation ofsaid tirst iin-driving means under the latter condition for controllingthe operation of said second tin-driving means.

3. in a ship stabilization system, a nn, a first mounting means forsupporting said iin on a ship to rotate about a first axis extendinggenerally longitudinally of said fin and normally in a generallyhorizontal direction, a second mounting means for supporting said iin topivot about a second axis normally extending in a generally verticaldirection, a rst drive means coupled with said lirst mounting means forrotating said lin about said rst axis and a second drive means coupledwith said second mounting means for pivoting said iin about said secondaxis, means for producing a signal in accordance with rolling motions ofsaid ship, means coupled with said iin for obtaining a repeat-backsignal proportional to the lift exerted on said ship by said iin,control means coupled with said first drive means for controlling thesame in accordance with said roll signal, means coupled with said iinfor producing a signal in accordance with the position of said tin aboutsaid rst axis and manually operable means coupled with said first iindrive means, said first and second drive means for controlling saidfirst drive means in accordance with said position signalonly and forcontrolling said second drive means in dependence upon a predeterminedposition of said iin about said iirst axis.

4. In a ship stabilization system, a pair of stabilizing :tins mountedone on each side of the ship, means for supporting said tins forrotation about axes thereof extending generally outwardly from the shipwhereby rotation of said tins about said axes serves to produce a litton each side of 4said ship as the ship moves through the water, separatemeans coupled with each lin for respectively driving the same about saidaxes, means for obtaining signals dependent on roll motions of the ship,means coupled with each iin for obtaining independent repeatback signalsproportional to the lift exerted on each side of said ship by each iin,and means coupled with each drive means for independently controllingeach drive 14 means in accordance with said roll signals and itsrespective repeat-back signal.

5. In a roll stabilization system for ships, a pair of stabilizing nsmounted one on each side of the ship, means for supporting said lins forrotation aboutV axes thereof extending generally outwardly from the shipwhereby rotation of said ns about said axes serves to produce a lift oneach side of said ship as the-ship moves through the water, separatedrive means coupled with each iin for respectively driving said tinsabout Vsaid axes, means for obtaining signals dependent on roll motionsof the ship, means coupled with each drive means for independentlysupplying said roll signals to each of said driving means, meansresponsive to the separate operations of said ns for obtainingindependent repeat-back signals proportional to the magnitude anddirection of the lift exerted on each side of said ship by each of saidfins, and control meansrcoupled with each drive means for independentlycontrolling each drive means in ,accordance with its respective rollsignals and its respective repeat-back signal.

6. In a ship stabilization system, a iin, mounting means for supportingsaid iin on a ship to rotate about an axis extending generallylongitudinally of said fin and normally in a generally horizontaldirection, drive means coupled with said iin for rotating said iin aboutsaid axis, means for supplying a signal proportional to roll rate of theship, means for supplying a signal proportional to roll accelerations ofthe ship, means for supplying a signal proportional to the angle of rollof the ship with respect to the apparent vertical, means responsive toiin operation for obtaining a repeat-back signal proportional to thelift exerted by said iin, and control means responsive to all of saidsignals for controlling said drive means in accordance with thealgebraic sum thereof.

7.*In a ship stabilization system, a iin, mounting means for supportingsaid fin on a ship for rotation about an axis extending generallylongitudinally of said iin and normally in a direction substantially atright angles to the longitudinal axis of said ship, drive meansconnected to said tin for rotating the same about said iin axis, meansfor supplying signals proportional respectively to the roll angle, rollrate, and roll acceleration of Said ship, first servo means responsiveto said signals for supplying a lift command signal proportional to thealgebraic sum thereof, a second servo loop responsive to said liftcommand signal for controlling said iin drive means in accordancetherewith, means coupled with said iin for supplying a repeat-backsignal in accordance with the lift exerted on said ship by said tin, andmeans for additionally controlling said second servo loop in accordancewith said lift repeat-back signal.

8. Apparatus as set forth in claim 7, wherein said feedback signalfurther includes a signal which varies in accordance with thedisplacement of said iin with respect to said ship. l

9. In a ship stabilization system, a lin, mounting means for supportingsaid tin on a ship to rotate about an axis extending generallylongitudinally of said iin and normally in a generally athwartshipdirection, means for producing a signal in accordance with rollingmotions of said ship, a lirst servo loop responsive to said signal forproducing a lift command signal, means for limiting the output of saidViirst servo loop whereby to limit the magnitude of said commanded liftsignal, drive means having an output coupled with said tin for rotatingthe same about said axis,fmeans responsive to the operation of said tinfor producing a repeat-back signal proportional to the lift exerted onsaid ship by said iin, a second servo loop responsive to the sum of saidlift command signal and repeat-back signal for controlling said drivemeans in accordance with the algebraic sum thereof whereby to limit theactual lift of said fin to the limited value of said lift commandsignal.

l0. Apparatus as set forth in claim 9 further including means responsiveto the displacementV of said tins with respect to said ship for limitingtheY operation of said second servo loop independentlyof said commandedlift signal.

11. In a ship stabilization system, a iin, mounting means for supportingsaid n on a ship to rotate about an axis extending generallylongitudinally of said iin and normally in a generally horizontaldirection, means for producing a signal in accordance with rollingmotions of said ship, a iirst servo loop responsive to said signal forsupplying a lift command signal proportional thereto, means for limitingthe maximum value of the output of said iirst servo loop whereby tolimit the maximum value of said lift command signal,` drive means havingan output coupled with said lin for rotating the same about said axis,means for supplying a repeat-back signal proportional to the liftexerted on said ship by said lin, a second servo loop responsive to saidlimited command signal and said lift repeat-back signal for controllingsaid drive means in accordance with the difference therebetween, andmeans controlled byy said limiting means for varying the ratio of theoutput of said fin driving means to the value of said lift commandsignal. l

12. In a stabilization system for ships of the activated iin type, incombination, a hollow housing, having arms arranged generally in theform of a T bearing means for supporting one arm of said' housing in aship to rotate about a substantially vertical axis, a iin having atrunnion thereon, spaced bearings in the other arm of saidhousing forsupporting said. trunnion for rotation about a substantiallyhorizontally axis, drive means coupled with said trunnion for rotatingthe iin about said horizontal axis whereby to produce lifting couples onsaid ship through said one arm, and force measuring means within saidtrunnion for measuring the llexure of said trunnion produced betweensaid support` bearings by the iin lift transmitted thereto.

13. Apparatus as set forth in claim 13 wherein said last-mentioned meanscomprises a cantilever beam secured at one end thereof to said trunnionadjacent the bearing at one end of said trunnionand the other endthereof terminating adjacent the bearings supporting the other end ofsaid trunnion, and signal generating means coupled .between saidtrunnion and said other end of said beam for measuring the flexure ofsaid trunnion between said bearings produced by said lifting coupleswhereby to produce a signal proportional to the lift exerted on saidship by said iin.

14. The combination with a marine vessel of an antiroll fin rotatablysupported on said vessel and adapted to extend generally laterally ofsaid vessel and beneath the surface of the water, and fin control meansfor controlling the rotational position of said iin whereby to controlthe lift exerted by the fin on said vessel, said control means includingmotive means connected with said fin for rotating the same, inertialroll-rate responsive means for supplying a primary control signalproportional to the rate of roll of said vessel, servomotor meansconnected to be controlled by said roll rate signal for rotatablypositioning said iin, forceresponsive means coupled with said fin forsupplying a force signal proportional to the lift exerted .by said iinon said vessel, and means for feeding said force signal back incontrolling relation to said servomotor means in a sense to oppose saidprimary control signal whereby said iin is positioned such that thedetected roll rate is opposed by a substantially equal and oppositeinduced roll rate thereby to maintain the resultant roll rate of saidvessel substantially zero.

15. The combination set forth in claim 14 further comprising pendulousmeans for providing a secondary control signal in accordance with themagnitude of the deviations of the vertical axis of said vessel from theapparent vertical, and means for additionally supplying said sec- 16ondary control signal in controlling relation to said servomotor means.

16. The combination set forth in claim 14 further comprising inertialmeans responsive to roll accelerations of said vessel for providing afurther secondary control signal proportional to said rollaccelerations, and means for supplying said further secondary controlsignal to said servomotor means.

17. The combination set forth in claim 14 further comprising signallimiting means responsive to said primary control signal for limitingthe maximum value thereof whereby to limit the operation of saidservomotor means, and means coupled with said limiting means for varyingsaid maximum limit in accordance with ships speed.

18. The combination set forth in claim 17 further comprising additionallimiting means coupled with said iin and responsive to the magnitude ofthe rotational position thereof with respect to said vessel, and meanscoupled with said servomotor means and responsive to said additionallimiting means for limiting the maximum value of said rotationalposition of said tinA independently y of said control signal.

19. Apparatus for arresting rolling motions of a marine vessel of thetype having an underwater lin adapted upon tilt thereof to exert a rollmoment on said vessel when the vessel is under way, said-moment beingproduced by the force exerted on said iin as a result of the angle ofattack thereof relative to the direction of the resultant water velocityadjacent said iin, the direction of said resultant water velocity beingdependent on the relative magnitudes of not only horizontal componentsbut alsovertical components of water velocity with respect to saidvessel, and drive means for angularly positioning said fin with respectto said vessel, said apparatus comprising, inertia responsive meanscarried by said vessel for providing a primary control signalproportional to rate of roll of said vessel, control means coupled withsaid drive means and responsive to said primary control signal forrotationally positioning said iin with respect to said vessel, forceresponsive means coupled with said iin for producing a force signalproportional to the lift eX- erted on said iin by said resultant watervelocity whereby to provide a measure of the angle of attack of said finwith respect to said resultant water velocity, and means for supplyingsaid force signal to said control means in a sense to oppose saidprimary controlsignal whereby to position said iin with respect to saidship in accordance with the angle of attack of said n with respect tosaid resultant water velocity and thereby independently of the angularposition of said n with respect to said ship.

V2l). In a stabilization system for marine vessels of the activated tintype, the combination comprising a hollow housing having arms arrangedgenerally in the form of a T, a first pair of spaced bearing means forsupporting one arm of said housing in the vessel to rotate about asubstantially vertical axis, a iin having a trunnion thereon, a secondpair of spaced bearings in the other arm of said housing for supportingsaid trunnion for rotation about a substantially horizontal athwartshipaxis, drive means coupled with said iin trunnion for rotating theiin'about said horizontal axis whereby to produce lifting couples onsaid vessel through both of said spaced bearing means, and forcemeasuring means associated with one pair of said spaced bearing meansfor measuring the magnitude of the couple therebetween produced by theiin lift transmitted therethrough. l

Y 21. Apparatus as set forth in claim 20 wherein said force measuringmeans includes strain gauge means responsive to flexure of said trunnionbetween Said second pair of spaced bearing means.

22. Apparatus as set forth in claim 20 wherein said force measuringmeans includes strain gauge means coupled with one of said first pair ofbearings and responsive to the lift force produced therebetween.

23. In a ship stabilization system, the combination com-l prising a iinadapted to be rotated from a stowed position to a rigged-out positionand when so rigged-out to be tilted to produce righting couples on saidship when under weigh, a hollow housing having arms arranged generallyin the form of a T, one arm thereof supported in a ship for rotationabout a substantially vertical axis and having said tin supported in theother arm thereof for tilt about a substantially horizontal axis, tirstmotive means coupled between said ship and said housing for rotatingsaid housing about said vertical axis whereby to rotate said iin from astowed to a rigged-out position and vice versa, and second motive meanscarried by said housing for rotation therewith and including a finactuating coupling extending within said housing and engageable withsaid iin for tilting the same about said horizontal axis, said secondmotive means including an hydraulic ram secured to and rotatable withsaid iirst mounting means and having its drive axis coincident with saidvertical axis.

24. In a ship stabilization system, the combination comprising a iinadapted to be rotated from a stowed position to a rigged-out positionand when so rigged-out to be tilted to produce righting couples on saidship when under weigh, a hollow housing having arms arranged generallyin the form of a T, one arm thereof supported in a ship for rotationabout a substantially vertical axis and having said tin supported in theother arm thereof for tilt about a substantially horizontal axis, thelongitudinal axis of said iin being laterally spaced from said verticalaxis, iirst motive means coupled between said ship and said housing forrotating said housing about said vertical axis whereby to rotate saidiin from a stowed to a rigged-out position and vice versa, and secondmotive means carried by said housing for rotation therewith andincluding a n actuating coupling extending within said housing andengageable with said iin for tilting the same about said horizontalaxis, said second motive means including an hydraulic ram secured to androtatable with said first mounting means and having its drive axiscoincident with said vertical axis, said coupling means comprising aconnecting rod and crank between said ram and said iin for convertingthe linear motion of said ram along said drive axis to rotary motion ofsaid tin about said longitudinal axis.

25. In stabilization system for marine vessels of the activated rintype, in combination, a prefabricated box-like structure having top,bottom, and side walls, one of said side Walls having a n receivingopening therein-and adapted to be installed as a unit within the hull ofsaid vessel with said opening on the exterior thereof, a iinsupportinghousing having arms arranged generally in the form of a T, bearing meansin said upper and lower walls for supporting one arm of said housing torotate within said box about a substantially vertical axis, a iin,bearing means in the other arm of said housing for supporting said 1into rotate about a substantially horizontal axis, a first hydraulic ramsecured to and rotatable with said housing and having its drive axissubstantially coincident with said vertical axis and a crank arm coupledbetween said ram and said iin for rotating said n about said horizontalaxis, a second hydraulic ram means supported on the top w-all of saidbox-like structure and crank arms secured to said housing and coupledwith said second ram means for rotating said housing about said verticalaxis whereby to rotate said iin through said opening.

2.6. In a ship stabilization system, a iin, mounting means forsupporting said tin on a ship for rotation about an axis extendinggenerally longitudinally of said iin and normally in a directionsubstantially at right angles to the longitudinal axis of said ship,drive means connected to said iin for rotating the same about said iinaxis, means for supplying signals proportional respectively to the rollangle, roll rate, and roll acceleration of said ship, iirst servo meansresponsive to said signals for supplying a lift command signalproportional to the algebraic sum thereof, a second servo loopresponsive to said lift command signal for controlling said iin drivemeans in accordance therewith, means coupled with said iin for supplying`a rst repeat-back signal variable in accordance with the lift exertedon said ship by said iin, means also coupled with said tin for supplyingya second repeat-back signal variable in accordance with the angulardisplacement of said iin with respect to said ship, and means foradditionally controlling said second servo loop in accordance with saidtirst and second repeat-back signals.

References Cited in the tile of this patent UNITED STATES PATENTS967,565 Rohan Aug. 16, 1910 1,800,408 `Schein Apr. 14, 1931 2,188,834Fischel et al. Jan. 30, 1940 2,626,114 Alderson Ian. 20, 1953 2,638,288Hanna May 12, 1953 2,723,089 Schuck et al. Nov. 8, 1955 2,770,429 Schucket al Nov. 13, 1956 2,809,603 Bell Oct. 15, 1957 2,832,305 Bell Apr. 29,1958 FOREIGN PATENTS 515,665 France Nov. 27, 1920 581,776 Great BritainOct. 24, 1946 671,699 Germany Feb. 11, 1939 UNITED STATES PATENT UEEICEeeiirieii eoeemlv Patent No 2,9799010 April llv 1961 Frederick DuBraddon et elil It is hereby certified that error appears in the abovenumbered patent requiring correction and that the, said Letters Patentshould read as A corrected below,

' Column l line 25u for "tloef'U first oeourrehoewread to column ii,line 52 for 'illuetrtaed" read illustrated column 8u line 66g or 'life"read m lift Column 9v line 75, after "looking" insert me of -mg columnl0(J line 45V after "centering" insert H- the fin 2O.a Howevery es soonas the iin is so CenteredU en; column l3yI line 57I strike out "saidfirst iin drive means"; Column 15XI line 39Y for the Claim referencenumeral "13" read -nl2 wel,

Signed and sealed this 7th day of November 1961.,

(SEAL) Attest:

ERNEST W. SWTDER DAVTD E. LADD Attesting Officer Commissioner of PatensUSCGMM-DC

